This invention relates generally to semiconductor manufacturing methods and more particularly to masks, and the formation of masks, used in such manufacturing methods.
As is known in the art, fabrication of semiconductor integrated circuits involves transferring a sequence of patterns onto a surface of a semiconductor body. The patterns are formed by masks, each mask having a desired pattern. More particularly, an un-patterned mask is initially provided, such mask having: a transparent substrate, such as quartz; an opaque layer, such as chrome over the substrate; and, a layer of photoresist over the opaque layer. The photoresist is patterned with the desired pattern using an electron, or light beam. The patterned photoresist is then exposed to an etch which thereby exposes underlying portions of the opaque layer. That is, the pattern in the photoresist is transferred to the opaque layer. The exposed portions of the opaque layer are etched to expose underlying portions of the transparent substrate. The photoresist is then removed thereby forming the patterned mask.
As is also known in the art, the electron, or light beam process used to pattern the photoresist will not produce perfectly square corners; rather, the corners will be somewhat rounded. Further, the etching of the exposed portions of the opaque layer by a wet isotropic etch will result in lateral undercutting into the opaque layer, an effect sometimes referred to as edge process bias. These effects, i.e., corner rounding and edge process bias, can adversely effect the accuracy of the mask and hence the accuracy of the devices formed in the semiconductor body.
More particularly, the pattern fidelity in masks for small ground rule geometries, i.e., 250 nm and beyond, DRAM products is becoming an important quality parameter. One of the latest requirements in mask building is to monitor the amount of corner rounding on the mask. Corner rounding measurements, however, are difficult. Known methods are based on an optical inspection of checkerboard-type structures, or image processing of an SEM picture of a certain structure. The former is time consuming, not automatic, and strongly dependant on the operators skill; the latter requires an additional coating and clean step in addition to the SEM measurement. Another type of corner rounding measurement is based on a line shortening effect produced as a result of the corner rounding effect. Such measurement uses the length of the shortened line. Because these measurements are made over the small end portion of the structure, i.e., a test region of the mask, the reproducibility is relatively low and also strongly dependant on an operator taking the measurement.
A method is provided for determining a measure of corner rounding produced in a mask structure. The method includes providing an un-patterned mask structure having a transparent substrate, an opaque layer on the substrate, and a photoresist on the opaque layer. A corner rounding test pattern is etched (i.e., transferred) into the photoresist. The pattern exposes underlying portions of the opaque layer. The pattern is in the shape of a pair of intersecting perpendicular lines of the photoresist. The exposed portions of the opaque layer are brought into contact with an etch to remove the exposed portions of the opaque layer and to thereby expose underlying portions of the substrate. The photoresist is removed to produce mask structure. A defect (i.e., a corner rounding effect produced defect) is produced in the opaque layer of the mask structure, such defect being produced as a result of rounded corners, rather than square corners. The defect is formed in a region at the intersection of the pair of intersecting perpendicular lines of the photoresist. The defect is measured to provide an indication of the degree of corner rounding.
With such method, standard measuring equipment, such as line width measuring equipment or defect detecting equipment can be used to determine the degree of corner rounding produced in the mask.
In accordance with one embodiment, a method is provided for determining a measure of corner rounding produced in a mask structure. The method includes providing an un-patterned mask structure having a transparent substrate, an opaque layer on the substrate, and a photoresist on the opaque layer. A corner rounding test pattern is etched into the photoresist. The pattern exposes underlying portions of the opaque layer. The pattern is in the shape of a pair of intersecting perpendicular lines of the photoresist. The exposed portions of the opaque layer are brought into contact with a wet etch to remove the exposed portions of the opaque layer and to thereby expose underlying portions of the substrate. The etch undercuts the photoresist to remove unexposed portions of the opaque layer disposed adjacent to the exposed portions of the opaque layer. That is the isotropic etch etches laterally into the edges of the opaque layer (i.e., edge process bias). The photoresist is removed to produce mask structure. A defect (i.e., a corner rounding effect produced defect) is produced in the opaque layer of the mask structure, such defect being produced as a result of rounded corners, rather than square corners. The defect is formed in a region at the intersection of the pair of intersecting perpendicular lines of the photoresist. The defect is measured to provide an indication of the degree of corner rounding.
In accordance with another aspect of the invention, the intersecting lines of the photoresist have widths selected to produce a defect having a size related to the degree of the produced corner rounding.
In accordance with still another aspect of the invention, the measurement includes measuring the size of the produced defect.
In accordance with still another aspect of the invention, the width of one of the intersecting lines of the photoresist is greater than the width of the other one of the intersecting lines.
In accordance with one embodiment of the invention a method is provided for determining a measure of corner rounding produced in a mask structure. The method includes providing an un-patterned mask structure having a transparent substrate, an opaque layer on the substrate, and a photoresist on the opaque layer. A corner rounding test pattern is etched into the photoresist, such pattern exposing underlying portions of the opaque layer, such pattern being formed in a predetermined shape. The shape includes: a first line; and, an array of laterally spaced parallel lines, such parallel lines being perpendicular to, and intersecting, the first line at laterally spaced intersection regions along the first line. An etch is brought into contact with the exposed portions of the opaque layer to remove the exposed portions of the opaque layer. The photoresist is removed to produce the mask structure. The corner rounding effect defect produced in the opaque layer of the mask structure along the first line is measured. The defect is produced as a result of rounded corners, rather than square corners, being etched in forming the intersections along the first line by the array of parallel lines.
In accordance with one embodiment, the etch is an isotropic etch to remove the exposed portions of the opaque layer and to thereby expose is underlying portions of the substrate. The etch undercuts the photoresist to remove unexposed portions of the opaque layer disposed adjacent to the exposed portions of the opaque layer.
In accordance with another embodiment of the invention, a method is provided for determining a measure of corner rounding produced in a mask structure. Here again, an un-patterned mask structure is provided having a transparent substrate, an opaque layer on the substrate, and a photoresist on the opaque layer. A corner rounding test pattern is etched into the photoresist, such pattern exposing underlying portions of the opaque layer. The pattern comprising an array rectangular-shaped openings in the photoresist to expose underlying portions of the opaque layer. The rectangular-shaped openings are separated by a pair of intersecting lines of the photoresist. The exposed portions of the opaque layer are brought into contact with an etch to remove the exposed portions of the opaque layer to thereby expose underlying portions of the substrate. A first one of the lines of the photoresist separating the rectangular-shaped openings is in the order of the predetermined undercutting depth. The etching of the opaque layer forms a triangular-shaped region in the opaque layer as a result of corner rounding effects in forming the array of rectangular-shaped openings in the photoresist. The triangular-shaped region, i.e., a corner rounding effect produced defect, has an altitude along the first one of the lines of the photoresist and a base along a second one of the lines of the photoresist. The altitude is related to the amount of such corner rounding. The photoresist is removed to produce the mask structure. Variations in the width of the line of opaque layer are measured, such width variations being produced as a result of the altitude of the triangular-shaped region resulting from the rectangular-shaped opening in the photoresist being formed with rounded corners, rather than square corners.
In one embodiment, the etch undercuts the photoresist a predetermined depth as a result of etch process bias to remove unexposed portions of the opaque layer disposed adjacent to the exposed portions of the opaque layer.
In accordance with another embodiment of the invention, a method is provided for determining a measure of corner rounding produced in a mask structure. Here again, an un-patterned mask structure is provided having a transparent substrate, an opaque layer on the substrate, and a photoresist on the opaque layer. A corner rounding test pattern is etched into the photoresist, such pattern exposing underlying portions of the opaque layer. The pattern comprising an array rectangular-shaped openings in the photoresist to expose underlying portions of the opaque layer. The rectangular-shaped openings are separated by a pair of intersecting lines of the photoresist. The exposed portions of the opaque layer are brought into contact with a etch to remove the exposed portions of the opaque layer to thereby expose underlying portions of the substrate. Both of the lines of the photoresist separating the rectangular-shaped openings are in the order of the predetermined undercutting depth. The etching of the opaque layer forms a diamond-shaped region in the opaque layer as a result of corner rounding effects in forming the array of rectangular-shaped openings in the photoresist. The diamond-shaped region, i.e., a corner rounding effect produced defect, has a size related to the amount of such corner rounding. The photoresist is removed to produce the mask structure. Defect measuring equipment is used to detect and measure the size of the diamond-shaped region to thereby provide a measure of the corner rounding effect.
In one embodiment, the etch undercuts the photoresist a predetermined depth as a result of etch process bias to remove unexposed portions of the opaque layer disposed adjacent to the exposed portions of the opaque layer.